To MEMS (Micro Electro Mechanical Systems) such as a pressure sensor, an acceleration sensor, a gyrosensor, a micromirror and an optical modulator, and optical devices having a CCD element or a CMOS element applied, a package wherein the element portion is open to the above is employed (Patent Documents 1 and 2). Further, to achieve the downsizing and the weight saving of a semiconductor device such as an optical device or a MEMS, application of a packaging structure (such as chip size package (CSP)) wherein a sealing substrate comprising a semiconductor substrate, a glass substrate or the like is directly bonded to a semiconductor substrate having a sensor element, a CMOS element or the like provided, is in progress.
To bond a semiconductor substrate (a semiconductor substrate for an element) having a sensor element, a CMOS element or the like formed and a sealing substrate comprising a semiconductor substrate, a glass substrate or the like, a resin, a metal material such as Au—Sn solder, a glass material or the like is used. The sensor element, the CMOS element or the like provided on the semiconductor substrate for an element is required to be airtightly sealed, and particularly an element constituting the MEMS is commonly airtightly sealed in a vacuum state. Among the above-described bonding materials (sealing materials), the resin is poor in the airtightness, and thus it may decrease the reliability of the semiconductor device. Since the metal material such as Au—Sn solder has electrical conductivity, it cannot be directly formed on the semiconductor substrate when insulation is required, and it has such drawbacks that the production cost will increase so as to achieve an insulating package.
As the sealing material (sealing glass) comprising a glass material, usually low temperature melting PbO glass (lead glass) has been used. The sealing glass has such advantages that it is excellent in the airtight sealing properties, the moisture resistance, etc. and that it can directly be formed on the semiconductor substrate since it is an insulating material. However, it has such drawbacks that when a PbO sealing glass or the like having a conventional composition is used as a sealing material for a semiconductor device, components (metal oxides such as PbO) in the sealing glass will be reduced due to the semiconductor substrate (such as a Si substrate) and the atmosphere (particularly vacuum atmosphere) at the time of sealing, whereby metal balls will deposit, whereby the insulation of the semiconductor substrate will be reduced, thus leading to an increase in the surface leak.
To solve such problems, deposition of the metal due to reduction of the glass components (metal oxides) can be suppressed by lowering the sealing temperature (firing temperature of the sealing glass). However, a decrease in the sealing temperature will deteriorate the reactivity of the sealing glass with the semiconductor substrate, thus leading to a decrease in the bond strength and the reliability. Accordingly, in order to use the sealing glass as a sealing material for a semiconductor device, it is important to suppress the deposition of metals by reduction of the glass components (metal oxides) without decreasing the reactivity with and the adhesion to the semiconductor substrate.